Metastatic Clear Cell Renal Cell Carcinoma Identified in a Gastric Biopsy: Diagnostic Recognition in an Unusual Site

TL;DR

A rare case of kidney cancer found in a stomach biopsy highlights the need for careful diagnosis in unusual locations.

Contribution

Presents a rare case of metastatic ccRCC diagnosed via gastric biopsy before renal lesion sampling.

Findings

Gastric biopsy showed epithelioid cells with clear cytoplasm and delicate vasculature.

IHC staining confirmed renal origin with positivity for PAX8, RCC marker, and CD10.

Negative staining for CK7, CK20, CDX2, and TTF-1 excluded primary gastrointestinal or pulmonary tumors.

Abstract

Metastatic clear cell renal cell carcinoma (ccRCC) to the stomach is rare and may mimic other clear cell neoplasms when encountered in limited biopsy samples. We report a case in which a gastric biopsy provided the first histopathologic confirmation of metastatic ccRCC in a 65-year-old man who had not yet undergone tissue sampling of a suspected renal lesion. The biopsy showed nests of epithelioid cells with clear cytoplasm and delicate vasculature, and immunohistochemical (IHC) staining demonstrated strong positivity for paired box gene 8 (PAX8), renal cell carcinoma (RCC) marker, and CD10, supporting renal origin. Negative staining for cytokeratin 7 (CK7), cytokeratin 20 (CK20), caudal-type homeobox transcription factor 2 (CDX2), and thyroid transcription factor 1 (TTF-1) helped exclude primary gastric, gastrointestinal, and pulmonary neoplasms. Subsequent imaging confirmed a renal mass concordant with the IHC findings. This case underscores the importance of recognizing morphologic clues and using a targeted IHC panel when evaluating clear cell neoplasms in the gastrointestinal tract.

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